Numerous cameras are currently available that capture a sequence of images, and have a zoom feature that allows a user to progressively zoom into or out from interesting details. The zoom can be an optical zoom, a digital zoom, or a zoom comprising both optical and digital zooms. Various cameras include such zooms, including video cameras and camcorders (both analogue and digital), surveillance cameras, and digital and analogue “still” cameras that are arranged to capture sequences of still images and/or video sequences.
A zoom feature allows a camera to change from a long shot to a close-up shot (or vice versa). Historically, only an optical zoom (also termed mechanical zoom) was possible. An optical zoom normally utilizes a zoom lens in which the focal length is continuously variable while maintaining a fixed focal plane, so as to provide variable magnification of the subject.
In more recent years, electronic zooms have been developed. The electronic zooms enlarge or reduce a predetermined area of a picture by using electronic processing. This processing can be performed during the capture of the picture, or subsequently by the camera or even by utilizing post capture image processing software in editors. In many instances, electronic zooms (also referred to as digital zooms) also incorporate processing techniques to improve the image quality of the zoomed image e.g. by interpolating adjacent pixels.
While a zoom feature can be useful during filming, having a zooming action in a video sequence is normally considered bad practice. Virtually all professional and semi-professional productions (e.g. wedding videos) do not contain dramatic zooming actions in the final video. Some viewers find having a fast zoom action in a sequence to be disturbing. However, amateur users frequently tend to abuse the zoom feature and hence inevitably worsen the quality of the resulting video as perceived by a viewer.
When it is necessary to show a wide view followed by a more detailed view (or vice versa), the best practice is considered to be to change straight from the wide view to the detailed view rather than performing a zoom sequence.
Professional productions tend to utilize two or more cameras to achieve this effect, with the views suddenly switching from the camera with a wide viewing angle to a close up camera (or vice versa). This obviously requires the simultaneous use of two such cameras.
If only a single camera is utilized, then in order to achieve a change between a wide-angle view and a detailed view, the camera must zoom from one view to the other. Consequently, in order to edit the resulting image sequence to achieve an abrupt change from one view to another, it is necessary to cut out the zoom sequence and hence lose the intervening frames (and any associated audio track).
FIG. 1 is an illustration of such an editing process. Waveform 10 provides an indication of the level (i.e. amount) of the zoom of a camera as a function of time, with the frame sequence 20 illustrating the corresponding sequence of frames (A, B, C).
As can be seen, initially the camera is not zoomed in, and remains at a constant low magnification level producing frames A having a wide-angle view. Subsequently, the camera is progressively zoomed in producing frames B, until the zoom reaches an adequate level of detail after which the zoom remains constant so as to provide frames C at a constant magnified level of detail, i.e. zoom.
The resulting edited video and audio track 30 cuts directly from the wide-angle viewed frames A to the magnified viewed frames C, so as to omit the zooming action. It will thus be appreciated that the frames B containing the zooming action are lost, along with any associated audio track. Losing such information is undesirable.
EP 0853855, “Video Camera with Improved Zoom Capability”, attempts to address this problem by providing a zoom camera which uses a combination of electronic (i.e. digital) zoom and optical zoom so as to obtain a rapid change in magnification, and hence minimize the period of time during which the zoom sequence exists. While this approach minimizes the duration of the zoom sequence, the zoom sequence still exists.